GENERAL50879

• Permit No: M1978116
• IBM Index Class Name: General Documents
• Doc Date: 3/6/2006
• Doc Name: Third Review
• From: DMG hhp
• To: DMG
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Na[ural Resources
1313 Sherman St., Room 215 C O L O RA D O
Denver, Colorado 80203 D 1 v 1 5 1 0 N o f
Phone: [phone] MINERAL S
FAX: [phone]
C--E~II I~OcS
GEOLOGY
REC EAM ATION•NIN ING
EAf ETY•ECIENCE
Bill Owens
Govemar
Date: March 6, 2006
Russell George
Executive Direttor
To: Russ Means, Grand Junction Field Office Ronald W. Cottony
~/LJ~~~
~ ~~~~~~~
~ Division Director
Natural Resource Trustee
From:
Harry Posey
1
~
/
/
/
Kate Pickford
RE: / Third Review: DMO status. Cotter Corporation Uranium Mines, Montrose County:
JD-6 Mine, M-1977-310
~ C-JD-8 Mine, M-1984-014
~ JD-9 Mine, M-1977-306
'GSM-18 Mine, M-1987-116
This review responds to the February 7, 2006 (reed Feb 8) letter in "RE: Response to the January 17,
2006 letter from the Colorado Deparhnent of Mining and Geology (DMG)." In that letter, the Operator's
consultant, GeoScience Services, further explained and interpreted results of hydrologic modeling and
modeling assumptions pertinent to potential Designated Mining Operation (DMO) status for the above-
captionedmines. This review covers all previous submittals regarding DMO status by reference.
The applicant explained, and the Division accepts, that the model simulations evaluate dispersion and
diffusion, rather than dilution of potential contaminants in the unsaturated zone, and not necessarily the
saturated zone, beneath waste rock that has the potential to release acid and/or toxic substances to
groundwater, according to SPLP test results.
The Division considers the following features or assumptions as either acceptable or "conservative."
1. A "realistic" modeling approach would include the effects of sorption. By ignoring the potential
effects of sorption in the model, the model is "conservative."
2. The model assumes that waste rock piles would contribute a constant discharge under a constant
head. This is an acceptable means of handling the calculation for dispersion the unsaturated zone,
and simplifies the modeling without compromising its accuracy or utility.
3. The model assumes that waste rock piles will release contaminants to the unsaturated zone or
elsewhere in concentrations indicated by the SPLP results. This assumption is very conservative.
SPLP test results tend to overestimate contaminant concentrations for several reasons, namely:
a. the surface area of the test samples far exceeds that actually available in the field;
b, tumbling the samples for the SPLP test maximizes exposure between fluid and rock; and
c. tumbling produces some degree of autogenous grinding, which further increase surface and
exaggerates the contact between fluid and rock.
4. The model assumes that surface water inflow, into bedrock, which is comprised of mudstone,
siltstone and sandstone, equals 1/10 of the average annual rainfall. This is very conservative.
Office of Office of Colorado
Mined Land Reclamation Attive and Inactive Mines Geological Survey